1. Field of the Invention
The present invention relates to a medical laser apparatus for irradiating an affected tissue with a laser beam to treat the affected tissue.
2. Description of Related Art
As a laser apparatus capable of outputting a visible laser beam for treatment by continuous wave oscillation, for example, there is a known laser apparatus that converts an infrared laser beam as a fundamental wave emitted from an Nd:YAG laser source or the like to a visible laser beam as a second harmonic wave by a wavelength converting element and outputs the visible laser beam. In recent years, a laser apparatus is proposed, which shifts the infrared laser beam emitted from the Nd:YAG laser source or the like to a long wavelength side by a Raman fiber, converts the Raman-shifted infrared laser beam to a visible laser beam of orange color or red color which is preferable for photocoagulation treatment by a wavelength converting element, and outputs the visible laser beam.
It is desirable to output a visible laser beam for treatment used for ophthalmologic photocoagulation treatment or the like with high energy of 1 W or higher. However, a nonlinear crystal as a wavelength converting element for converting an infrared laser beam to a visible laser beam has a low damage threshold and cannot receive an infrared laser beam of high energy, so that it is difficult to output a visible laser beam of high energy. In addition, the spectral bandwidth (half width) of the Raman-shifted infrared laser beam tends to widen, so that the wavelength conversion efficiency of the wavelength converting element tends to deteriorate. Since the center wavelength of the Raman-shifted infrared laser beam easily fluctuates according to temperature and the like, the wavelength conversion efficiency of the wavelength converting element constructed so as to be adapted to a predetermined center wavelength also tends to deteriorate.